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Delineating Watersheds

Hi NatCappers,

I met must of you during the NatCap symposium earlier this year, hope everything is going well over there.  I've been trying to delineate my watersheds  for the SWY model. I've been having problems getting the right total
flow accumulation parameter to match the  stream output raster with the
watercourses dataset I have for my study region. I've been playing around with the TFA and distance to snap points and it just doesn't seem to be getting any closer. The polygons I'm getting are also very small, I think because I've just been getting multiple and small streams, scattered over the area.

I used a smaller subset of the region and it worked well (the stream output matched the watercourses dataset). I've been using the same parameters again TFA:  110,000 but its not working. I wonder what am I doing wrong this time. Could you please have a look and give me some advice? 

I'm using a 1 sec Hydrologically enforced DEM, projected to GDA94_Australian_Albers

My data on this google drive folder, both the inputs I'm using and an example of the results I've got:

Thank you so much!!!


  • swolnyswolny Member, NatCap Staff
    Hi Jaramar -

    It looks like you're using DelineateIt to create the watersheds.If you get multiple small streams (it actually looks like you hardly have any streams at all), that is probably the problem. I've learned that just because something calls itself a "hydrologically enforced DEM" doesn't mean that it produces good streams when you process it, which is annoying. Have you tried filling pits in the DEM? We recommend QGIS Wang & Liu, it does a good job. Give it a try and see if it helps create a continuous stream network. If it does, then hopefully your watersheds will look better too. 

    ~ Stacie

  • Hi Stacie,

    Thank you so much for pointing that out. I certainly thought pits were already  filled  in the DEM I was using, but no. I used QGIS Wang and Liu and now I'm getting a nice stream network and watersheds. Thank you!!

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